The present invention relates to a method for converting a feed including an oxygenate to a product including a light olefin, in which supplemental heat is added with a heating fuel having low autoignition temperature, low sulfur, and low nitrogen content.
Light olefins, defined herein as ethylene, propylene, butylene and mixtures thereof, serve as feeds for the production of numerous important chemicals and polymers. Particularly, light olefins are used in the manufacture of polyolefins such as polypropylene and polyethylene. Catalysts for polyethylene and polypropylene require a product that is substantially free of contaminants such as sulfur and nitrogen. When sulfur and nitrogen compounds are present in the olefin feedstock, the catalyst is rendered less effective resulting in poorer quality goods or less efficient polymerization products.
One emerging technology for the production of light olefins uses oxygenate feedstocks such as methanol, ethanol or dimethyl ether. Methanol, ethanol and dimethyl ether feedstocks are produced from synthesis gas derived from natural gas or other sources. Oxygenate feedstocks produced from this method are desirable because they contain negligible amounts of nitrogen or sulfur and result in olefin products that are less poisonous to polymerization catalysts. One embodiment of the reaction of oxygenates to olefins uses a molecular sieve catalyst, such as a SAPO catalyst, in a reactor system that has an oxygenate to olefin (xe2x80x9cOTOxe2x80x9d) reactor and a catalyst regenerator. The catalyst in the OTO reactor converts oxygenates to olefins and also generates and deposits carbonaceous material (coke) on the molecular sieve catalysts used to catalyze the conversion process. Over accumulation of these carbonaceous deposits will interfere with the catalyst""s ability to promote the reaction. Thus, the molecular sieve catalyst is periodically recycled to the catalyst regenerator. During regeneration, the coke is removed from the catalyst by combustion with oxygen, which restores the catalytic activity of the catalyst. The regenerated catalyst is then recycled back to the OTO reactor where it is reused to catalyze the OTO reaction.
U.S. Pat. Nos. 6,023,005 and 6,166,282, both of which are incorporated herein by reference, disclose methods of producing ethylene and propylene by catalytic conversion of oxygenate in a fluidized bed reaction process which utilizes catalyst regeneration.
U.S. Pat. Nos. 4,595,567, and 4,615,992, both of which are incorporated herein by reference, disclose general and specific regeneration devices and techniques.
The reactor system comprising an OTO reactor and a regenerator often requires the addition of heat to the reactor system. The OTO reaction is exothermic, requiring an initial heating to initiate the reaction, after which it is self-sustaining. There are also periods where the oxygenate feed must be interrupted, at which time it would be desirable to keep the reactor and regenerator hot. In addition, the initial start-up of the regenerator and heating of the catalyst also requires heat.
Conventionally, the regenerator apparatus is preheated by an auxiliary burner which burns a starting fuel such as natural gas with air to provide a heated gas that contains air and gaseous combustion products such as carbon dioxide and water (steam), to the regenerator. The auxiliary burner can be associated with the regenerator air blower that introduces the heated gas through an air inlet at the bottom of the regenerator. However, given the low heat capacity of such heated gas, resulting in part from its expansion upon heating, the heat input to the unit is limited. Particularly, the maximum amount of heat and the maximum temperature is limited. When heat is added to reactors other than OTO reactor systems, such as a fluid catalytic cracking (FCC) system, hydrocarbon feed (gas oil) to the FCC unit is burned in the regenerator to heat the catalyst. However, the gas oil feedstock of an FCC unit is contaminated with nitrogen and sulfur and would be unsuitable in an OTO process, as the gas oil would increase the levels of these contaminants in the products. Methanol is undesirable as a fuel for heating catalyst because it has a high autoignition temperature, and igniting and sustaining the burning of methanol would be difficult. The process of fluid catalytic cracking (FCC) normally circulates hot catalyst from the regenerator to the reactor to add heat to the reactor. One method of doing this combusts a fuel with the air feed to the regenerator. The FCC process normally uses fuel gas (including natural gas), or a combination of fuel gas and heavy liquid feedstock for this purpose. The fuel gas is combusted in an auxiliary burner, located after the air blower but before entering the fluidized bed of catalyst in the regenerator. The limited heat capacity of the regeneration air, resulting in part from its expansion upon heating, limits the rate at which heat is added to the regenerator through this method. It is normally desirable to add heat at a greater rate, and thus a liquid fuel, normally consisting of gas oil feedstock, is added to the fluidized catalyst zone. The catalyst has a much higher heat capacity than the combustion air, and thus liquid fuel can be added at a much greater rate in the fluidized catalyst zone than can be added to the combustion air through the auxiliary burner. The gas oil also has a relatively low autoignition temperature of 315-370xc2x0 C. (600-700xc2x0 F.), which aids in the initiation of combustion, as well as helping to ensure that the combustion will not be extinguished during a low temperature excursion.
In trying to adapt the FCC heating method to the MTO process, some major problems are encountered. Gas oil cannot be used as the heating fuel, because the sulfur and nitrogen introduced by the gas oil cannot be tolerated in the MTO product recovery section. The MTO feedstock, methanol, cannot be used as the heating fuel, because its autoignition temperature of 468xc2x0 C. (875xc2x0 F.) is so high that preheating the catalyst bed in the regenerator to a sufficient temperature to initiate the combustion of methanol is difficult. Also, there is a greater risk of extinguishing the burn from a low temperature excursion.
Accordingly, it would be desirable to provide a process for making olefins from oxygenate which has an initiation procedure which provides a high heat input to an oxygenate to olefins reactor system within a reasonable time, hours rather than days, to provide supplemental heat to the reactor, without contaminating either the OTO catalyst or the MTO products and byproducts. The present invention satisfies these and other needs.
The present invention solves the current needs in the art by providing a method for converting a feed including an oxygenate to a product including a light olefin.
The method of the present invention is conducted in a reactor apparatus. As used herein, the term xe2x80x9creactor apparatusxe2x80x9d refers to an apparatus which includes at least a place in which an oxygenate to olefin conversion reaction takes place. As further used herein, the term xe2x80x9creaction zonexe2x80x9d refers to the portion of a reactor apparatus in which the oxygenate to olefin conversion reaction takes place and is used synonymously with the term xe2x80x9creactor.xe2x80x9d Desirably, the reactor apparatus includes a reaction zone, an inlet zone and a disengaging zone. The xe2x80x9cinlet zonexe2x80x9d is the portion of the reactor apparatus into which feed and catalyst are introduced. The xe2x80x9creaction zonexe2x80x9d is the portion of the reactor apparatus in which the feed is contacted with the catalyst under conditions effective to convert the oxygenate portion of the feed into a light olefin product. The xe2x80x9cdisengaging zonexe2x80x9d is the portion of the reactor apparatus in which the catalyst and any additional solids in the reactor are separated from the products. Typically, the reaction zone is positioned between the inlet zone and the disengaging zone.
The present invention relates to a process for making an olefin product from an oxygenate feedstock in the presence of an oxygenate to olefin molecular sieve catalyst which comprises:
a) contacting at least a portion of the catalyst with a regeneration medium in a regeneration zone;
b) heating said regeneration zone to a first temperature of at least 225xc2x0 C. (437xc2x0 F.), e.g., at least 260xc2x0 C. (500xc2x0 F.),
c) feeding to said regeneration zone a heating fuel having an autoignition temperature less than the first temperature and containing less than 500 wppm sulfur, e.g., less than 100 wppm sulfur, and less than 200 wppm nitrogen, e.g., less than 100 wppm nitrogen, thereby causing the heating fuel to ignite and provide a heated catalyst; and
d) circulating said heated catalyst to the reaction zone; and
e) additionally contacting the feedstock in a reaction zone with said oxygenate to olefin molecular sieve catalyst including said heated catalyst, under conditions effective to convert the feedstock into an olefin product stream.
In one embodiment, the olefin product stream comprises C2-C3 olefins.
In still another embodiment of the invention, the conditions employed are effective to form carbonaceous deposits on the catalyst.
In still another embodiment, the catalyst is heated to at least 316xc2x0 C. (600xc2x0 F.) in the regeneration zone prior to the step of feeding the heating fuel.
In yet another embodiment of the invention, the regeneration zone has a fuel inlet and an air inlet capable of providing an airflow through the regeneration zone, located upstream from the fuel inlet in relation to direction of the airflow, and the process further comprises (1) combusting a starting fuel with an air stream from said air inlet thereby imparting sufficient heat content within the regeneration zone to obtain the first temperature at or near the fuel inlet and (2) feeding the heating fuel through the fuel inlet.
In still another embodiment, the starting fuel employs a carbonaceous gas, e.g., natural gas.
In yet another embodiment of the invention, the starting fuel has an autoignition temperature of greater than about 482xc2x0 C. (900xc2x0 F.).
In another embodiment, the process of the invention further comprises filling the regeneration zone with the catalyst to a level sufficient to cover said fuel inlet before the combusting step (1), and adding additional catalyst after step (2) of feeding the heating fuel, to provide additional heated catalyst.
In still another embodiment, the catalyst is heated to at least 316xc2x0 C. (600xc2x0 F.) in the regeneration zone prior to the feeding step (2). heated to at least 316xc2x0 C. (600xc2x0 F.)
In another embodiment, the heating fuel is a liquid fuel.
In still another embodiment, at least 50 wt % of the heating fuel is a C11-C20 hydrocarbon fraction.
In another embodiment, at least 75 wt % of the heating fuel is a C11-C20 hydrocarbon fraction.
In still another embodiment, at least 85 wt % of said heating fuel is a C11-C20 hydrocarbon fraction.
In another embodiment, at least 75 wt % of the heating fuel is a C12-C19 hydrocarbon fraction and further said heating fuel has an autoignition temperature ranging from 232xc2x0-271xc2x0 C. (450xc2x0-520xc2x0 F.) and contains less than 10 wppm sulfur and less than 10 wppm nitrogen.
In yet another embodiment, at least 75 wt % of the heating fuel is a C12 to C16 hydrocarbon fraction.
In another embodiment, at least 75 wt % of the heating fuel is a C12 to C14 hydrocarbon fraction.
In still another embodiment, the reaction zone is cooled by steam injection.
In another embodiment, the reaction zone comprises a riser.
In yet another embodiment, the reaction zone comprises plural risers.
In still yet another embodiment, the reaction zone has two risers.
In yet another embodiment, the catalyst comprises molecular sieve having a pore diameter of less than 5.0 Angstroms.
In still yet another embodiment, the catalyst comprises at least one molecular sieve framework-type selected from the group consisting of AEI, AFT, APC, ATN, ATT, ATV, AWW, BIK, CAS, CHA, CHI, DAC, DDR, EDI, ERI, GOO, KFI, LEV, LOV, LTA, MON, PAU, PHI, RHO, ROG, THO, ZSM-5, ZSM-4, SAPO-34, SAPO-17, SAPO-18, MeAPSO and substituted groups thereof.
In yet another embodiment, the catalyst comprises a molecular sieve having a pore diameter of 5-10 Angstroms.
In still yet another embodiment, the catalyst comprises at least one molecular sieve framework-type selected from the group consisting of MFI, MEL, MTW, EUO, MTT, HEU, FER, AFO, AEL, TON, and substituted groups thereof.
In another embodiment, the heating step (b) occurs before the contacting step (e).
In still another embodiment, the heating step (b) occurs concurrent with the contacting step (e).
In yet another embodiment, first contacting step (a) occurs before the heating step (b).
In still another embodiment, the heating fuel contains less than 10 wppm, e.g., less than 5 wppm, sulpher and less than 10 wppm, e.g., less than 5 wppm, nitrogen.
In yet another embodiment, the invention relates to a method of adding heat to a reactor system having an oxygenate to olefin reaction zone and a catalyst regeneration zone wherein catalyst is cycled from the reaction zone to the regeneration zone and from the regeneration zone to the reaction zone, the method comprising:
fluidizing catalyst in the regeneration zone in the presence of an oxygen containing gas;
heating the catalyst in the regeneration zone to a first temperature;
introducing a heating fuel into the regeneration zone wherein the heating fuel has about 100 wppm or less of sulfur and has about 100 wppm or less nitrogen and an autoignition temperature greater than the first temperature but no greater than about 482xc2x0 C. (900xc2x0 F.) to provide a heated catalyst; and
provide the heated catalyst into the reaction zone.
In yet another embodiment of the invention described immediately above, the process further comprises: contacting the catalyst with an oxygenate feedstock under conditions sufficient to convert said oxygenate to an olefin-rich product.
In still another embodiment of the invention described immediately above, the invention further comprises the process wherein said heating fuel contains a total of no greater than 20 wppm of metal selected from the group consisting of nickel and vanadium.
In yet another embodiment, the invention relates to a process for initially increasing the temperature of a reactor system for making an olefin product from an oxygenate feedstock in the presence of an oxygenate to olefin molecular sieve catalyst which process comprises:
a) contacting at least a portion of the catalyst with a regeneration medium in a regeneration zone;
b) heating said regeneration zone to a first temperature of at least 225xc2x0 C. (437xc2x0 F.),
c) feeding to said regeneration zone a heating fuel having an autoignition temperature less than the first temperature and containing less than 100 wppm sulfur and less than 100 wppm nitrogen, thereby causing the heating fuel to ignite and provide a heated catalyst; and
d) circulating said heated catalyst to the reaction zone.
In still another embodiment of the invention described immediately above, the invention comprises the process which further comprises:
e) additionally contacting the feedstock in a reaction zone with said oxygenate to olefin molecular sieve catalyst including said heated catalyst, under conditions effective to convert the feedstock into an olefin product stream.
These and other advantages of the present invention shall become apparent from the following detailed description, the attached FIGURE and the appended claims.